On-demand operations

ABSTRACT

Many applications and computing environments allow users to migrate data from a source object to a target object (e.g., a file may be cut/pasted, copied, etc.). It may be advantageous to provide users with access to the data (e.g., migrated data at the target object and/or data that has yet to be migrated from the source object) before all of the data is completely migrated (e.g., a user may otherwise have to wait hours for a 2 TB file to be copied between various data volumes). Accordingly, as provided herein, migration of a source object to a target object may be declared as completed, even though the target object may not comprise all of the data that is to be migrated. In this way, an I/O request may be satisfied based upon migrated data within the target object and/or data, not yet migrated, retrieved on-demand from the source object.

FIELD

The instant disclosure pertains to facilitating on-demand operations ona target data object, such as a file, migrated from a source dataobject, notwithstanding the target data object comprising less than allof the data of the source data object that is to be migrated from thesource data object to the target data object.

BACKGROUND

Business entities and consumers are storing an ever increasing amount ofdigitized data. For example, many commercial entities are in the processof digitizing their business records and/or other data. Similarly, webbased service providers generally engage in transactions that areprimarily digital in nature. Thus, techniques and mechanisms thatfacilitate efficient and cost effective storage of vast amounts ofdigital data are being implemented. For example, a cluster networkenvironment of nodes may be implemented as a data storage system thatfacilitates the storage, retrieval, and/or processing of data. The datastorage system may comprise one or more data storage devices configuredto store user data within data volumes, for example. In this way, theuser data may be stored, accessed, migrated, and/or processed within thedata storage system.

Data may be frequently migrated (e.g., copied, cut/pasted, restored,replicated, backed up, etc.) within the data storage system and/orbetween data storage systems. In one example, a user may cut and pastefiles, folders, and/or directories from a first data volume to a seconddata volume. In another example, a data replication service mayreplicate a data volume across one or more nodes, such as computingdevices, within the data storage system. In another example, a user maycopy a file from a local data storage device to a mobile storage device,such as a flash drive. Unfortunately, migrating large amounts of datamay consume resources (e.g., CPU utilization, processing time, networkbandwidth, etc.). Additionally, the original data and/or the migrateddata may be unavailable until the migration is completed (e.g., all datafrom the source data object is migrated to the target data object). Forexample, a user may migrate a source data volume comprising 2.5 TB ofdata from a source location to a target data volume at a targetlocation. During the migration of the 2.5 TB of data, the source datavolume and/or the target data volume may be unavailable (e.g., a usermay be unable to read from and/or write to the 2.5 TB of data).

SUMMARY

This disclosure relates to one or more techniques and/or systems forfacilitating on-demand operations at a data object level, such as at afile granularity. It may be appreciated that a source data object maycomprise data that is to be migrated into a target data object (e.g., asource text document may be copied, cut/pasted, restored, replicated,etc. to create a target text document). Normally, the migration may bedeclared as completed once all of the data from the source data objectis migrated into the target data object. During migration, the data maybe unavailable to the user until the migration is complete (e.g., a usermay be unable to read/write to the target data object because the targetdata object may not comprise all of the migrated data until themigration is completed). However, as provided herein, the migration maybe declared as being completed before all of the data of the source dataobject is completely migrated into the target data object (e.g., thetarget text document may be declared as completely migrated even thoughthe target text document may comprise less than all of the data that isto be migrated from the source text document into the target textdocument). In this way, the target data object may appear to be migratedand/or available to a user, even though less than all of the data hasbeen migrated into the target data object (e.g., the target textdocument may comprise 1 MB out of 4.5 MB of data that is to be migratedfrom the source text document).

Accordingly, I/O requests, such as read/write requests, associated witha target data object may be performed before all of the data of a sourcedata object is fully migrated into the target data object. If the I/Orequest is associated with migrated data comprised within the targetdata, then the I/O request may be satisfied by the migrated data withinthe target data object. If the I/O request is associated with data notyet migrated to the target data object, then an on-demand operation maybe performed to retrieve the data from the source data object to satisfythe I/O request. For example, a target text document may comprise afirst portion of data migrated from a source text document, but may notyet comprise a second portion of data that is to be migrated from thesource text document. A read operation for the target text document maybe associated with the second portion of data not yet migrated into thetarget text document. As provided herein, the read operation may besatisfied even though the target text document does not comprise thesecond portion of data because an on-demand operation may be performedto retrieve the second portion of data from the source text document. Inparticular, the second portion of data may be retrieved from the sourcetext document on-demand to satisfy the read operation.

In one example, a request to migrate a source data object from a sourcelocation to a target location may be received. A target data objectcorresponding to the source data object may be generated. The targetdata object may initially comprise less than all of the data of thesource data object. For example, the target data object may compriseinformation that the target data object is associated with the sourcedata object, how to access the source data object, how to access arelationship between the source data object and the target data object,migrated data from the source data object, and/or other informationregarding the migration. A relationship between the source data objectand the target data object may be specified, which may describe thesource data object, the target data object, and/or information regardingthe migration, for example. The relationship may specify fetchinformation for the source data object (e.g., the fetch information maycomprise a source path, such as a file system path, and/or a source dataobject handle, such as a file handle, used to access the source dataobject). It may be appreciated that the relationship may be used tofetch data from the source data object on-demand to satisfy an I/Orequest (e.g., read/write operations) for the target data object, wherethe data associated with the I/O request has yet to be migrated from thesource data object to the target data object. The relationship maycomprise an indication of what data has been migration and/or what datahas yet to be migrated. For example, the relationship may maintain ablock, multi-block, etc. level mapping that maps data blocks from thesource data object to data blocks at the target data object (e.g., asource data object may comprise a plurality of data blocks having a oneto one mapping with a plurality of data blocks of the target dataobject). As the target data object's data blocks are filled withmigrated data from corresponding data blocks of the source data object,the block level mapping may be updated to indicate that such data blocksare filled.

The source data object may be declared as being migrated to the targetlocation as the target data object notwithstanding the target dataobject comprising less than all of the data of the source object that isto be migrated from the source data object to the target data object.For example, the target data object may appear to a user as comprising100% of the data of the source data object, even though the target dataobject may merely comprise 5% of the data that is to be migrated fromthe source data object to the target data object. In this way, themigration may appear to a user as occurring quicker than what themigration may otherwise take to complete (e.g., a move operation, suchas a copy/paste operation, of a 2.5 TB file may appear to be migratedalmost instantaneously). Thus, the user may perform I/O requests, suchas read or write requests, on the target data object regardless ofwhether the target data object comprises data associated with the I/Orequests. It may be appreciated that data may be migrated from thesource data object to the target data object even though the migrationmay have been declared as completed (e.g., the remaining 95% of thesource data may be migrated over time to the target data object as abackground task).

In one example of satisfying an I/O request, a read request to accessread data associated with a target data object may be received. If thetarget data object comprises the read data, then the read request may besatisfied using the read data from the target data object. If the targetdata object does not comprise the read data associated with the readrequest, then an on-demand operation may be performed to fetch the readdata from a corresponding source data object. In particular, fetchinformation for the source data object may be determined from arelationship of the source data object and the target data object. Forexample, a source data object handle (e.g., a file handle) for thesource data object may be used to locate and/or access the source dataobject to retrieve the read data that has not yet been migrated. In oneexample, an on-demand operation may be performed to retrieve the readdata from the source data object to fill the target data object usingthe fetch information. The read request may be performed upon the readdata filled within the target data object.

In another example, a write request to create written data associatedwith the target data object may be received. The write request may beperformed upon the target data object to generate written data (e.g.,which may or may not overwrite data already migrated or written to thetarget data object). An instruction may accompany the write requestspecifying not to overwrite the written data with subsequently migrateddata from the source data object, where such an instruction may bespecified within the relationship of the source data object and thetarget data object, for example. In this way, the user may perform writeoperations upon the target data object that may not be overwritten withsubsequently migrated data from the source data object.

It may be appreciated that data from the source data object may betransferred (migrated) to the target data object in order to satisfy themigration request. In one example, the migration of data may occurwithout notification to a user that the migration is occurring. Instead,the user may be provided with an indication that the migration has beencompleted (e.g., the migration may be declared as completed), eventhough it may still be occurring. Additionally, an indication of thesource data object may be removed from the source location. In this way,it may appear to a user that the migration of the source data object tothe target data object has completed, even though data may still bepending for migration from the source data object to the target dataobject. Thus, user interactions with the target data object may besatisfied with on-demand operations without the user having to waituntil the migration is fully completed.

To the accomplishment of the foregoing and related ends, the followingdescription and annexed drawings set forth certain illustrative aspectsand implementations. These are indicative of but a few of the variousways in which one or more aspects may be employed. Other aspects,advantages, and novel features of the disclosure will become apparentfrom the following detailed description when considered in conjunctionwith the annexed drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in accordance with one or more of the provisions set forthherein.

FIG. 2 is a component block diagram illustrating an example data storagesystem in accordance with one or more of the provisions set forthherein.

FIG. 3 is a flow chart illustrating an exemplary method of facilitatingdata object level on-demand operations.

FIG. 4 is a flow chart illustrating an exemplary method of maintaining arelationship mapping at a target location.

FIG. 5 is a component block diagram illustrating an exemplary system forfacilitating data object level on-demand operations.

FIG. 6 is an illustration of an example of a migration componentmigrating source files to target files and specifying relationshipsbetween respective source and target files.

FIG. 7 is an illustration of an example of an on-demand componentfacilitating a write request associated with a target file.

FIG. 8 is an illustration of an example of an on-demand componentfacilitating a read request associated with a target file.

FIG. 9 is an example of a computer readable medium in accordance withone or more of the provisions set forth herein.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the claimed subject matter.It may be evident, however, that the claimed subject matter may bepracticed without these specific details. Nothing in this detaileddescription is admitted as prior art.

Today, users may create, store, share, and/or utilize much informationas electronic data. Consumers and business entities may store such dataacross various data volumes, data storage devices, and/or computingdevices. For example, a cluster network environment may comprise aplurality of nodes configured to provide access to user data storedwithin data storage devices of the cluster network environment (e.g.,data storage devices 128, 130 may comprise volumes 132 of user data asillustrated in FIG. 1). The stored data may be accessible through dataoperations, such as read or write operations. In one example, data maybe migrated from a source location to a target location through a copyfunction, a cut/paste function, a replication function, a restorefunction, a cloning function (e.g., a single file clone operation),and/or through other functionality. Migration of large amounts of datamay take a significant amount of time before completion (e.g.,restoration of a backup file comprising 200 GB of data from a first datavolume to a second data volume may take hours). Unfortunately, themigrated data (e.g., a source data object and/or a target data object)may be unavailable until the migration is completed. For example, a usermay restore a 200 GB backup file from a storage server to a local clientdevice. The user may have to wait until the migration of the entire 200GB is completed before having access to the migrated backup file,regardless of whether the user merely wishes to access a small portionof the backup file (e.g., 10 MB portion).

Accordingly, one or more techniques and/or systems for facilitating dataobject level on-demand operations, which may be used to satisfy I/Orequests, are provided herein. In particular, migration operations(e.g., copy, cut/paste, move, backup, restore, etc.) of a source dataobject to a target data object may be declared as completed before allof the data has been migrated. In this way, the migration operation mayappear to be highly efficient to a user (e.g., the migration operationof large amounts of data may appear to be migrated almostinstantaneously). Additionally, the target data object (e.g., migrateddata within the target data object and/or data that has yet to bemigrated to the target data object) may be available to the user eventhough the target data object may comprise less than all of the datafrom the source data object that is to be migrated (e.g., the targetdata object may comprise merely a few megabytes out of 2 gigabytes ofdata that is to be migration from the source data object). I/O requestsfrom the user to access the data may be satisfied through on-demandoperations that may fetch corresponding data from the source data objectas necessary. For example, a read request may correspond to data thathas yet to be migrated to a target data object, thus the data may beretrieved from the source data object to satisfy the read request. Inthis way, the user may read, write, and/or interact with the target dataobject notwithstanding the target data object comprising less than allof the data of the source data object that is to be migrated.

To provide a context for an embodiment for facilitating data objectlevel on-demand operations, FIG. 1 illustrates a cluster networkenvironment 100, for example, which may comprise source locations andtarget locations between which data may be migrated and/or on-demandoperations may be performed to satisfy I/O requests, and FIG. 2illustrates an embodiment of a data storage system that may beimplemented to facilitate data migration and/or on-demand operations ofdata stored therein, for example. It will be appreciated that where thesame or similar components, elements, features, items, modules, etc. areillustrated in later figures but were previously discussed with regardto prior figures, that a similar (e.g., redundant) discussion of thesame may be omitted when describing the subsequent figures (e.g., forpurposes of simplicity and ease of understanding).

FIG. 1 is a block diagram illustrating an example clustered networkenvironment 100 that may implement some embodiments of the techniquesand/or systems described herein. The example environment 100 comprisesdata storage systems 102 and 104 that are coupled over a cluster fabric106, such as a computing network embodied as a private Infiniband orFibre Channel (FC) network facilitating communication between thestorage systems 102 and 104 (and one or more modules, component, etc.therein, such as, nodes 116 and 118, for example). It will beappreciated that while two data storage systems 102 and 104 and twonodes 116 and 118 are illustrated in FIG. 1, that any suitable number ofsuch components is contemplated. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, in one embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while in another embodiment a clustered networkcan include data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more clients 108, 110 which maycomprise, for example, personal computers (PCs), computing devices usedfor storage (e.g., storage servers), and other computers or peripheraldevices (e.g., printers), are coupled to the respective data storagesystems 102, 104 by storage network connections 112, 114. Networkconnection may comprise a local area network (LAN) or wide area network(WAN), for example, that utilizes Network Attached Storage (NAS)protocols, such as a Common Internet File System (CIFS) protocol or aNetwork File System (NFS) protocol to exchange data packets.Illustratively, the clients 108, 110 may be general-purpose computersrunning applications, and may interact with the data storage systems102, 104 using a client/server model for exchange of information. Thatis, the client may request data from the data storage system, and thedata storage system may return results of the request to the client viaone or more network connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, for example. Such a node in a data storage andmanagement network cluster environment 100 can be a device attached tothe network as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

As illustrated in the exemplary environment 100, nodes 116, 118 cancomprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise a network module 120, 122 (e.g., N-Module, or N-Blade) anda data module 124, 126 (e.g., D-Module, or D-Blade). Network modules120, 122 can be configured to allow the nodes 116, 118 to connect withclients 108, 110 over the network connections 112, 114, for example,allowing the clients 108, 110 to access data stored in the distributedstorage system. Further, the network modules 120, 122 can provideconnections with one or more other components through the cluster fabric106. For example, in FIG. 1, a first network module 120 of first node116 can access a second data storage device 130 by sending a requestthrough a second data module 126 of a second node 118.

Data modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, data modules 124, 126 communicate with the data storage devices128, 130 according to a storage area network (SAN) protocol, such asSmall Computer System Interface (SCSI) or Fiber Channel Protocol (FCP),for example. Thus, as seen from an operating system on a node 116, 118,the data storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the example embodiment 100illustrates an equal number of N and D modules, other embodiments maycomprise a differing number of these modules. For example, there may bea plurality of N and/or D modules interconnected in a cluster that doesnot have a one-to-one correspondence between the N and D modules. Thatis, different nodes can have a different number of N and D modules, andthe same node can have a different number of N modules than D modules.

Further, a client 108, 110 can be networked with the nodes 116, 118 inthe cluster, over the networking connections 112, 114. As an example,respective clients 108, 110 that are networked to a cluster may requestservices (e.g., exchanging of information in the form of data packets)of a node 116, 118 in the cluster, and the node 116, 118 can returnresults of the requested services to the clients 108, 110. In oneembodiment, the clients 108, 110 can exchange information with thenetwork modules 120, 122 residing in the nodes (e.g., network hosts)116, 118 in the data storage systems 102, 104.

In one embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. Volumes can span a portion of a disk, acollection of disks, or portions of disks, for example, and typicallydefine an overall logical arrangement of file storage on disk space inthe storage system. In one embodiment a volume can comprise stored dataas one or more files that reside in a hierarchical directory structurewithin the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the example environment 100, the clients 108, 110 can utilize thedata storage systems 102, 104 to store and retrieve data from thevolumes 132. In this embodiment, for example, the client 108 can senddata packets to the N-module 120 in the node 116 within data storagesystem 102. The node 116 can forward the data to the data storage device128 using the D-module 124, where the data storage device 128 comprisesvolume 132A. In this way, in this example, the client can access thestorage volume 132A, to store and/or retrieve data, using the datastorage system 102 connected by the network connection 112. Further, inthis embodiment, the client 110 can exchange data with the N-module 122in the host 118 within the data storage system 104 (e.g., which may beremote from the data storage system 102). The host 118 can forward thedata to the data storage device 130 using the D-module 126, therebyaccessing volume 132B associated with the data storage device 130.

FIG. 2 is an illustrative example of a data storage system 200,providing further detail of an embodiment of components that mayimplement one or more of the techniques and/or systems described herein.The example data storage system 200 comprises a node 202 (e.g., hostnodes 116, 118 in FIG. 1), and a data storage device 234 (e.g., datastorage devices 128, 130 in FIG. 1). The node 202 may be a generalpurpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A client 205(e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provides access to files and/or other datastored on the data storage device 234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 236. The storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202 can to respond to clientrequests to manage data on the data storage device 200 (e.g., oradditional clustered devices) in accordance with these client requests.The operating system 208 can often establish one or more file systems onthe data storage system 200, where a file system can include softwarecode and data structures that implement a persistent hierarchicalnamespace of files and directories, for example. As an example, when anew data storage device (not shown) is added to a clustered networksystem, the operating system 208 is informed where, in an existingdirectory tree, new files associated with the new data storage deviceare to be stored. This is often referred to as “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software program code and data structures.The processors 204 and adapters 210, 212, 214 may, for example, includeprocessing elements and/or logic circuitry configured to execute thesoftware code and manipulate the data structures. The operating system208, portions of which are typically resident in the memory 206 andexecuted by the processing elements, functionally organizes the storagesystem by, among other things, invoking storage operations in support ofa file service implemented by the storage system. It will be apparent tothose skilled in the art that other processing and memory mechanisms,including various computer readable media, may be used for storingand/or executing program instructions pertaining to the techniquesdescribed herein. For example, the operating system can also utilize oneor more control files (not shown) to aid in the provisioning of virtualmachines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to aclient 205 over a computer network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The client 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the client 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the host 202 to access information requested by the client205. The information may be stored on any type of attached array ofwriteable media such as magnetic disk drives, flash memory, and/or anyother similar media adapted to store information. In the example datastorage system 200, the information can be stored in data blocks on thedisks 224, 226, 228. The storage adapter 214 can includes input/output(I/O) interface circuitry that couples to the disks over an I/Ointerconnect arrangement, such as a storage area network (SAN) protocol(e.g., Small Computer System Interface (SCSI), iSCSI, hyperSCSI, FiberChannel Protocol (FCP)). The information is retrieved by the storageadapter 214 and, if necessary, processed by the one or more processors204 (or the storage adapter 214 itself) prior to being forwarded overthe system bus 236 to the network adapter 210 (and/or the cluster accessadapter 212 if sending to another node in the cluster) where theinformation is formatted into a data packet and returned to the client205 over the network connection 216 (and/or returned to another nodeattached to the cluster over the cluster fabric 215).

In one embodiment, storage of information on arrays 218, 220, 222 can beimplemented as one or more storage “volumes” 230, 232 that are comprisedof a cluster of disks 224, 226, 228 defining an overall logicalarrangement of disk space. The disks 224, 226, 228 that comprise one ormore volumes are typically organized as one or more groups of RAIDs. Asan example, volume 230 comprises an aggregate of disk arrays 218 and220, which comprise the cluster of disks 224 and 226.

In one embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, such as data (D) and/or parity (P), whereas thedirectory may be implemented as a specially formatted file in whichother files and directories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume, which may also be referred to as a “traditionalvolume” in some contexts, corresponds to at least a portion of physicalmemory whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalmemory locations, such as some available space from each of the disks224, 226, 228. It will be appreciated that since a virtual volume is not“tied” to any one particular storage device, a virtual volume can besaid to include a layer of abstraction or virtualization, which allowsit to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In one embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent each volume stored ona data storage device, a target address on the data storage device canbe used to identify one or more LUNs 238. Thus, for example, when thehost 202 connects to a volume 230, 232 through the storage adapter 214,a connection between the host 202 and the one or more LUNs 238underlying the volume is created.

In one embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the LUNs 238.

Among other things, one or more systems and/or techniques forfacilitating data object level on-demand operations, such as at a filegranularity, are disclosed herein. On-demand operations may be performedto retrieve data from a source data object that has yet been migrated toa target data object in order to satisfy an I/O request for the targetdata object. That is, a source data object may be migrated to a targetdata object. Before the data of the source data object is fully migratedto the target data object, the migration may be declared as completedeven though the target data object may not comprise all of the data thatis to be migrated. Thus, I/O requests for the target data object thatinvolve data that has yet been migrated may be satisfied by performingan on-demand operation to retrieve the data from the source data object.In one example, such target data objects and/or source data objects maybe stored within data storage system 200 of FIG. 2 and/or data storagesystems 102, 104 of FIG. 1 (e.g., a source data object may be a filestored within a file system implemented within data storage system 200).Accordingly, the one or more systems and/or techniques disclosed hereinmay be implemented to facilitate on-demand operations to retrieve datastored within such data storage systems in order to satisfy I/Orequests.

In one example of facilitating on-demand operations within clusternetwork environment 100 of FIG. 1, a client 108 may initiate a migrationof a 200 GB source file from source volume 132B within source data storedevice 130 to target volume 132A within target data store device 128(e.g., where the source and target volumes 132A, 132B are in differentgeographic locations and/or the data store devices 128, 130 are indifferent geographic locations). In particular, a target filecorresponding to the source file may be generated within target volume132A. The target file may initially comprise less than all of the 200 GBof data that is to be migrated from the source file to the target file(e.g., the target file may comprise 15 GB out of the 200 GB data that isto be migrated). It may be advantageous to provide client 108 withaccess to the target file (e.g., located in San Francisco) withouthaving to wait for the entire 200 GB of data to be migrated from thesource file (e.g., located in San Diego) to the target file, which maytake hours. Thus, the migration may be declared as completed even though185 GB of data is still pending to be migrated from the source file tothe target file. Accordingly, the user may perform I/O requests to readfrom and/or write to the target file (e.g., the entire 250 GB of data)regardless of whether the data has been migrated to the target file. I/Orequests that may be satisfied by data migrated to the target file maybe directed to the target file for execution. I/O requests correspondingto data that has yet to be migrated to the target file may be satisfiedby retrieving the data on-demand from the source file.

One embodiment of facilitating data object level on-demand operations isillustrated by an exemplary method 300 at FIG. 3. At 302, the methodstarts. It may be appreciated that in one example, an I/O request maycorrespond to a read/write request for a target data object, and that anon-demand operation may be performed to retrieve data from a source dataobject that has yet to be migrated to the target data object in order tosatisfy the I/O request. It may be appreciated that in one example, asource data object and/or a target data object may comprise a singlefile.

At 304, a request to migrate a source data object from a source locationto a target location may be received. In one example, the request may bea source data object copy operation to copy a source data object at asource location to a target data object at a target location (e.g., arequest to copy a source text file to a target text file). In anotherexample, the request may be a source data object move operation tocut/paste a source data object at a source location to a target dataobject at a target location (e.g., a request to cut/paste a sourcespreadsheet file to a target spreadsheet file). In another example, therequest may be a source data object restoration operation to restore asource data object at a source location to a target data object at atarget location (e.g., a request to restore a source backup file to atarget location).

It may be appreciated that the source data object may correspond to asource path (e.g., Volume A: dan\workfiles\backupfiles) and the targetdata object may correspond to a target path (e.g., Volume D: backup)different than the source path. In one example, the source path maycorrespond to a first volume and the target path may correspond to asecond volume different than the first volume. Thus, on-demandoperations may be performed to satisfy I/O requests for data objects,such as files, that are migrated between different volumes. In anotherexample, the source path may correspond to a first computing device andthe target path may correspond to a second computing device differentthan the first computing device. Thus, on-demand operations may beperformed to satisfy I/O requests for data objects, such as files, thatare migrated between different computing devices.

At 306, a target data object corresponding to the source data object maybe generated at the target location. The target data object mayinitially comprise less than all of the data of the source data object.In one example, a request to migrate (e.g., cut/paste) a sourcespreadsheet file of 150 MB to a target spreadsheet file may be received.The target spreadsheet file may be generated, such that the targetspreadsheet file may initially comprise 3 MB of data. For example, 3 MBof data may comprise data specifying that the target spreadsheet file isto be migrated from the source spreadsheet file, an indication that thetarget spreadsheet file comprises less than all of the data that is tobe migrated, fetch information of the source spreadsheet file, locationof a relationship corresponding to the migration, data migrated from thesource spreadsheet file, and/or other information regarding themigration. It may be appreciated that the 150 MB may at some point befully migrated from the source spreadsheet file to the targetspreadsheet file to fully satisfy the migration request.

At 308, a relationship between the source data object and the targetdata object may be specified. The relationship may specify fetchinformation for the source data object and/or other informationregarding the migration. In one example, the relationship may bespecified within a data structure separate from the target data object,such as within a relationship mapping implemented as a B+ tree, forexample. It may be appreciated that the relationship may be used tofetch data from the source data object on-demand to satisfy an I/Orequest to access (e.g., read/write) data associated with the targetdata object that has not yet been migrated from the source data objectto the target data object.

At 310, the source data object may be declared as being migrated to thetarget location as the target data object notwithstanding the targetdata object comprising less than all of the data of the source dataobject that is to be migrated from the source data object to the targetdata object. For example, the target data object may appear to a user ascomprising 100% of the data of the source data object, even though thetarget data object may merely comprise 5% of the data that is to bemigrated from the source data object to the target data object. In oneexample, an indication of the target data object at the target locationmay illustrate the target data object as comprising the data of thesource data object as though the migration was actually completed, eventhough the target data object may comprise less than all data of thesource data object that is to be migrated. In another example, anindication of the source data object at the source location may beremoved (e.g., if the migration operation comprises a cut/pasteoperation, then the indication of the source data object may be removedto illustrate to a user that the cut has been performed, even though notall of the data has yet been cut/migrated from the source data object).

It may be appreciated that data may be migrated from the source dataobject to the target data object even though the migration may have beendeclared as completed. In one example, data transfer may begin after thegeneration of the target data object. In another example, data transfermay be delayed until such data is requested by an on-demand operation.In another example, data transfer may be delayed until appropriateresources, such as bandwidth and/or processing power, are available.

Because the migration may have been declared as completednotwithstanding the target data object comprising less than all of thedata of the source data object that is to be migrated, at 310, thetarget data object may appear to be accessible to a user (e.g., thetarget data object may appear to comprise 100% data of the source dataobject). Thus, the user may submit I/O requests for the target dataobject. In this way, read requests and/or write requests associated withthe target data object may be satisfied based upon data within thetarget data object and/or data within the source data object fetch byon-demand operations to the source data object. In one example, a readoperation for data that has already been migrated to the target dataobject may be satisfied with the migrated data within the target dataobject. In another example, a read operation for data that has not yetbeen migrated to the target data object may be satisfied by fetching thedata from the source data object using an on-demand operation, which mayutilize the relationship between the target data object and the sourcedata object (e.g., the relationship may specify fetch information thatmay be used to retrieve the data from the source data object).

In one example of a read request for data that has not yet been migratedto the target data object, the read request associated with the targetdata object may be received. It may be determined that the target dataobject does not comprise read data associated with the read request. Forexample, the target data object may comprise an indication that the readdata has not yet been migrated from the source data object to the targetdata object. Fetch information for the source data object comprising theread data may be determined from the relationship of the target dataobject and the source data object (e.g., the fetch information maycomprise a source data object handle, such as a file handle, of thesource data object, such as a source file). An on-demand operation maybe performed to fill the target data object with the read data from thesource data object based upon the fetch information. The read requestmay be performed upon the read data filled within the target object. Inthis way, the read request associated with the target data object may besatisfied, even though the target data object may not initially comprisethe read data.

In one example of a read request for data that has been migrated to thetarget data object, the read request associated with the target dataobject may be received. It may be determined that the target data objectmay comprise read data associated with the read request. For example,the read data may have been migrated to the target data object from thesource data object. The read request may be performed upon the read datawithin the target data object.

In one example of a write request associated with data that has not yetbeen written to the target data object from the source data object, thewrite request associated with the target data object may be received. Inone example, it may be determined that the write request is associatedwith data that has yet to be written to the target data object from thesource data object. The write request may be performed upon the targetdata object to generate written data. Because the written data may bemore up-to-date (less stale) than corresponding data within the sourcedata object that is to be migrated to the target data object, it may bespecified within the relationship that migrated data from the sourcedata object is not to overwrite the written data. In this way, the usermay write data to the target data object without the written data beingoverwritten by stale data that has yet to be migrated to the target dataobject from the source data object.

In one example of a write request corresponding to data that has beenmigrated to the target data object, the write request associated withthe target data object may be received. In one example, it may bedetermined that the write request is associated with data that has beenmigrated to the target data object from the source data object. Thewrite request may be performed upon the target data object to generatewritten data (e.g., new data may be generated within the target dataobject or migrated data within the target data object may be overwrittenby the write request). In this way, the user may write data to thetarget data object even though the target data object may not compriseall of the data of the source data object that is to be migrated (e.g.,60% of the source data object may be pending data that has yet to bemigrated to the target data object).

At 312, the method ends.

In another embodiment of facilitating on-demand operations, a request toaccess a portion of a target data object may be received. Adetermination that the target data object may be associated with amigration operation may be made based upon the target data objectcomprising at least one absent, empty, null, etc. data block. That is,the target data object may be associated with a migration operationwhere data of a source data object may be migrated into the target dataobject (e.g., a cut/paste operation of the source data object to thetarget data object). However, the target data object may comprise absentdata blocks if some of the data that is to be migrated has not yet beenmigrated (e.g., approximately 15% data of the source data object hasbeen migrated to the target data object, such that approximately 85%data of the source data object has yet to be migrated, and thus thetarget data object may comprise approximately 85% absent data blocks andapproximately 15% filled data blocks). It may be appreciated that arelationship may have been specified between the migration of the sourcedata object and the target data object. The relationship may comprise asource path of the source data object, which may be used to locate andaccess the source data object. In one example, the target data objectmay comprise an indication of the relationship (e.g., the target dataobject may specify that the target data object is associated with themigration operation and that a relationship exists that may be used todetermine additional information regarding the migration operation).

In one example, if the requested portion corresponds to one or moreabsent data blocks (e.g., a block of data at the target data object thathas not yet been filled with migrated data from the source data object)and the request corresponds to a read request, then a relationshipassociated with the migration operation between the source data objectand the target data object may be consulted (e.g., a user may request toaccess/read data from the target data object that has not yet beenmigrated the target data object, and thus an on-demand operation may beperformed to fulfill the read request with data from the source dataobject). The target data object may comprise an indication and/orlocation for the relationship. The relationship may be consulted todetermine the source path of the source data object, which may be usedto access the source data object. The read request may be satisfied byperforming an on-demand operation to retrieve data associated with theone or more absent data blocks from the source data object using thesource path. The retrieved data from the source data object may be usedto fill at least some of the one or more absent data blocks within thetarget data object. The filled data may be used to satisfy the readrequest.

If the requested portion corresponds to one or more absent data blocksand the request correspond to a write request, then the write requestmay be performed upon the target data object to generate written data.An indication that migrated data from the source data object is not tooverwrite the written data may be specified within the relationship.

If the requested portion corresponds to one or more filled data blocksand the request corresponds to a write request, the write request may beperformed upon the target data object to generate written data withinthe filled data blocks (e.g., an overwrite operation).

It may be appreciated that data may be migrated from the source dataobject to the target data object in various manners. In one example,data may be migrated over time (e.g., a background task may migratedata). In another example, data may be migrated in response to on-demandoperations. It may be appreciated that in one example, the migration ofdata may be tracked at various granularities within the relationship(e.g., a percentage of data migration may be tracked; particular blocksof migrated data may be tracked; etc.). In this way, the relationshipmay be updated as data migration occurs. Additionally, the relationshipmay be used to prioritize the order of data migration.

One embodiment of maintaining a relationship mapping at a targetlocation is illustrated by an exemplary method 400 at FIG. 4. At 402,the method starts. At 404, a first relationship between a first sourcedata object (e.g., a first backup file) at a first location and a firsttarget data object at a target location may be specified within arelationship mapping. It may be appreciated that the first source dataobject and the first target data object may be associated with amigration request to migrate the first source data object to the firsttarget data object (e.g., copy, cut/paste, restore, etc.). The firstrelationship may indicate that the first target data object comprisesless than all of the data of the first source data object that is to bemigrated from the first source data object to the first target dataobject. That is, the migration may be declared as being completed eventhough there may be pending data that has yet to be migrated from thesource data object to the target data object. In this way, the migrationmay appear to be highly efficient to a user (e.g., the migration mayappear to be completed almost instantaneously even though merely aportion of the data may be migrated so far). It may be appreciated thatthe pending data may at some point be migrated from the first sourcedata object to the first target data object to fully satisfy themigration request. The first relationship may comprise fetch informationfor the first source data object. It may be appreciated that the firstrelationship, such as the fetch information, may be used to fetch datafrom the first source data object on-demand to satisfy an I/O requestfor the first target data object involving data that has not yet beenmigrated from the first source data object to the first target dataobject.

At 406, the first relationship may be maintained (e.g., accessed,updated, deleted, etc.) within the relationship mapping based upon datamigration from the first source data object to the first target dataobject. In one example, the first relationship may provide an indicationof what data has been migrated from the first source data object to thefirst target data object and/or what data has yet to be migrated fromthe first source data object to the first target data object (e.g., ablock level mapping). The first relationship may be consulted todetermine which blocks of data of the first target data object have beenfilled with migrated data and/or which blocks of data of the firsttarget data object have yet to be filled with migrated data. In thisway, the first relationship may be consulted to determine whether dataassociated with an I/O request has been migrated or not. In anotherexample, what data is already migrated from the source data object tothe target data object and what data has not yet been migrated may bestored within a volume (e.g., comprising the target data object) bymarking particular blocks accordingly (e.g., as either migrated or not).

It may be appreciated that I/O requests for the first target data objectmay be performed regardless of whether the first target data objectcomprises all of the data of the first source data object that is to bemigrated from the first source data object to the first target dataobject. That is, the migration may be declared as completed (even thougheven though there may be pending data to migrate in order to fullysatisfy a migration request), such that the user may perform I/Orequests that may be satisfied based upon data within the first targetdata object and/or data within the first source object retrievedon-demand. In one example, an I/O request for the first target dataobject may be directed to the first target data object based upondetermining within the first relationship that the first target dataobject comprises data associated with the I/O request (e.g., a writerequest, a read request associated with data already migrated to thefirst target data object, and/or other requests that may be satisfiedthrough access to the first target data object). In another example, anI/O request for the first target data object may be directed to thefirst source data object based upon determining within the firstrelationship that the first target data object does not comprise dataassociated with the I/O request (e.g., a read request associated withdata that has yet to be migrated to the first target data object). TheI/O request may be facilitated (satisfied) by fetching the data from thefirst source data object based upon the fetch information for the firstsource data object. Additionally, the first target data object may befilled with the fetched data, thus advancing the migration of the firstsource data object to the first target data object.

It may be appreciated that an I/O request may correspond to dataassociated with the first target data object (e.g., data alreadymigrated to the first target data object) and data associated with thefirst source data object (e.g., data that has yet to be migrated to thefirst target data object). Such an I/O request may be satisfied basedupon directing the I/O request to the first target data object and tothe first source data object.

It may be appreciated that one or more relationships may be maintainedwithin the relationship mapping (e.g., one or more source data objectsmay be migrated to target data objects at the target location). In oneexample, a second relationship between a second source data object at asecond source location and a second target data object at the targetlocation may be specified within the relationship mapping. The secondrelationship may indicate that the second target data object comprisesless than all of the data of the second source data object. The secondrelationship may comprise fetch information for the second source dataobject. The second relationship may be maintained within therelationship mapping based upon data migration from the second sourcedata object to the second target data object. It may be appreciated thatthe second relationship may be used to fetch data from the second sourcedata object on-demand to satisfy a request to access (e.g., read/write)data associated with the second target data object that has not yet beenmigrated from the second source data object to the second target dataobject. It may be appreciated that the first source location and thesecond source location may be different locations. For example, thefirst relationship may correspond to a first source backup file locatedwithin a first data volume and the second relationship may correspond toa second source backup file located within a second data volumedifferent than the first data volume.

In another example, a third relationship between a third source dataobject at the first (and/or a different) source location (e.g., thefirst source location comprising the first source data object) and athird target data object at the target location may be specified withinthe relationship mapping. The third relationship may indicate that thethird target data object comprises less than all of the data of thethird source data object. The third relationship may comprise fetchinformation for the third source data object. The third relationshipwithin the relationship mapping may be maintained based upon datamigration from the third source data object to the third target dataobject. It may be appreciated that the third relationship may be used tofetch data from the third source data object on-demand to satisfy arequest to access (e.g., read/write) data associated with the thirdtarget data object that has not yet been migrated from the third sourcedata object to the third target data object.

In one example of a relationship mapping, the relationship mapping maycomprise a tree structure (e.g., a data structure, a B+ tree, etc.). Thetree structure may comprise source data object handles (e.g., filehandles used to access files) as indexes for respective relationshipswithin the relationship mapping. At 408, the method ends.

FIG. 5 illustrates an example of a system 500 configured to facilitatedata object level on-demand operations. The system 500 may comprise amigration component 502 and/or an on-demand component 504. The migrationcomponent 502 may be configured to receive a request to migrate 522 asource data object 514 (e.g., a 1.25 GB single file) from a sourcelocation 512 to a target location 508. In one example, the sourcelocation 512 may correspond to a first volume and the target location508 may correspond to a second volume different than the first volume.The migration component 502 may generate a target data object 510 at thetarget location 508. The target data object 510 may correspond to thesource data object 514 (e.g., the target data object 510 may be a copyof the source data object 514).

The target data object 510 may initially comprise less than all of thedata of the source data object 514 (e.g., the target data object 510 maycomprise 5 MB out of 1.25 GB of data from the source data object 514that is to be migrated). The migration component 502 may be configuredto declare the source data object 514 as migrated to the target location508 as the target data object 510 notwithstanding the target data object510 comprising less than all of the data of the source data object 514that is to be migrated from the source data object 514 to the targetdata object 510. That is, the migration 522 may be declared as beingcompleted even though there may be pending data to migrate from thesource data object 514 to the target data object 510. In this way, themigration 522 may appear to be highly efficient to a user (e.g., themigration 522 may appear to be completed almost instantaneously eventhough merely a portion of the data may be migrated so far). It may beappreciated that the pending data may at some point be migrated 522 fromthe source data object 514 to the target data object 510 to fullysatisfy the migration request. That is, the pending data may be migrated522 from the source data object 514 to the target data object 510 eventhough the migration may have been declared as completed.

The migration component 502 may specify 516 a relationship 518 betweenthe target data object 510 and the source data object 514. For example,the relationship 518 may be specified 516 within a relationship mapping506. The relationship 518 may specify fetch information for the sourcedata object 514 (e.g., a file handle that may be used to access thesource data object 514). It may be appreciated that the relationship 518may be used to fetch data from the source data object 514 on-demand tosatisfy a request to access (e.g., read/write) data associated with thetarget data object 510 that has not yet been migrated from the sourcedata object 514 to the target data object 510.

In one example, the on-demand component 504 may be configured to receivea read request associated with the target data object 510. The on-demandcomponent 504 may determine that the target data object 510 does notcomprise read data associated with the read request. The on-demandcomponent 504 may determine fetch information 520 for the source dataobject 514 comprising the read data based upon the relationship 518. Theon-demand component 504 may perform an on-demand operation to fill thetarget data object 510 with the read data from the source data objectbased upon the fetch information 520. In this way, the target dataobject 510 may comprise the read data associated with the read request.The on-demand component 504 may perform the read request upon the readdata filled within the target data object 510.

In another example, the on-demand component 504 may be configured toreceive a write requested associated with the target data object 510.The on-demand component 504 may perform the write request upon thetarget data object 510 to generate written data. The on-demand component504 may specify within the relationship 518 that migrated data from thesource data object 514 is not to overwrite the written data. In thisway, the write request may be perform locally to the target data object510 without being overwritten by migrated data (e.g., stale data) duringsubsequent migration.

FIG. 6 illustrates an example 600 of a migration component 602 migrating604 source files to target files and specifying relationships 608between respective source and target files. A first source location 612,such as a first data volume, may comprise source file (A) 616, sourcefile (B) 618, and/or other files. Source file (A) 616 may comprise 1 GBof data. Source file (B) 618 may comprise 2.5 TB of data. A secondsource location 614 may comprise a source file (C) 620 and/or otherfiles. Source file (C) 620 may comprise 500 MB of data. In one example,the first source location, the second source location, and/or the targetlocation may be different locations, such as different data volumes.

In one example, the migration component 602 may receive a request tomigrate source file (A) 616 from the first source location 612 to targetlocation 610 (e.g., migration 604). The migration component 602 maygenerate target file (A) 622 at the target location 610 (e.g., generatetarget files 606). The target file (A) 622 may initially comprise lessthan all of the date of the source file (A) 616 that is to be migratedfrom the source file (A) 616 to the target file (A) 622 (e.g., targetfile (A) 622 may comprise 405 MB out of 1 GB of data that is to bemigrated). The migration component 602 may declare the migration ofsource file (A) 616 to target file (A) 622 as completed notwithstandingthe target file (A) 622 as comprising less than all of the data of thesource file (A) 616 that is to be migrated. In this way, it may appearto a user that target file (A) 622 is accessible because the migrationwas declared as complete even though the migration is not actuallycomplete (e.g., the pending 595 MB of data may be migrated to the targetfile (A) 622 to actually complete the migration). The migrationcomponent 602 may specify a relationship 630 of target file (A) 622 andsource file (A) 616 within a relationship mapping 628. The relationshipmay comprise fetch information, such as a file handle for the sourcefile (A) 616, which may be used to access the source file (A) 616 tosatisfy I/O requests associated with target file (A) 622 correspondingto data that has yet to be migrated from source file (A) 616 to targetfile (A) 622.

In another example, the migration component 602 may receive a request tomigrate source file (B) 618 from the first source location 612 to targetlocation 610 (e.g., migration 604). The migration component 602 maygenerate target file (B) 624 at the target location 610 (e.g., generatetarget files 606). The target file (B) 624 may initially comprise lessthan all of the date of the source file (B) 618 that is to be migratedfrom the source file (B) 618 to the target file (B) 624 (e.g., targetfile (B) 624 may comprise 15 MB out of 2.5 TB of data that is to bemigrated). The migration component 602 may declare the migration ofsource file (B) 618 to target file (B) 624 as completed notwithstandingtarget file (B) 624 comprising less than all of the data of the sourcefile (B) 618 that is to be migrated. In this way, it may appear to auser that target file (B) 624 is accessible because the migration wasdeclared as complete even though the migration is not actually complete(e.g., the pending 2.5 TB of data may be migrated to the target file (B)624 to actually complete the migration). The migration component 602 mayspecify a relationship 632 of target file (B) 624 and source file (B)618 within a relationship mapping 628. The relationship may comprisefetch information, such as a file handle for the source file (B) 618,which may be used to access the source file (B) 618 to satisfy I/Orequests associated with target file (B) 624 corresponding to data thathas yet to be migrated from source file (B) 618 to target file (B) 624.

In another example, the migration component 602 may receive a request tomigrate source file (C) 620 from the second source location 614 totarget location 610 (e.g., migration 604). The migration component 602may generate target file (C) 626 at the target location 610 (e.g.,generate target files 606). The target file (C) 626 may initiallycomprise less than all of the date of the source file (C) 620 that is tobe migrated from the source file (C) 620 to the target file (C) 626(e.g., target file (C) 626 may comprise 1 MB out of 500 MB of data thatis to be migrated). The migration component 602 may declare themigration of source file (C) 620 to target file (C) 626 as completednotwithstanding target file (C) 626 comprising less than all of the dataof the source file (C) 620 that is to be migrated. In this way, it mayappear to a user that target file (C) 626 is accessible because themigration was declared as complete even though the migration is notactually complete (e.g., the pending 499 MB of data may be migrated tothe target file (C) 626 to actually complete the migration). Themigration component 602 may specify a relationship 634 of target file(C) 626 and source file (C) 620 within a relationship mapping 628. Therelationship may comprise fetch information, such as a file handle forthe source file (C) 620, which may be used to access the source file (C)620 to satisfy I/O requests associated with target file (C) 626corresponding to data that has yet to be migrated from source file (C)620 to target file (C) 626.

In one example, a relationship within the relationship mapping 628 maycomprise a mapping that maps data, such as at a block, multi-block, etc.granularity, of a source file to data of a target file. The mapping mayindicate which blocks of data of the target file have been filled withmigrated data and/or which blocks of data of the target file have yet tobe filled with migrated data. In this way, the relationship may be usedto determine whether an I/O request may be satisfied with migrated dataat the target file and/or with data that has yet to be migrated from thesource file. In another example, a relationship may comprise an IPaddress, a host name, and/or a computing device identifier (e.g., acluster wide node identifier) of a source location comprising a sourcedata object.

FIG. 7 illustrates an example 700 of an on-demand component 702facilitating a write request 714 associated with a target file (A) 710.It may be appreciated that the target file (A) 710 may correspond tosource file (A) 706 at source location 704. In particular, target file(A) 710 may have been generated at target location 708 in response to arequest to migrate source file (A) 706 to target file (A) 710 (e.g.,move, cut/paste, copy, restore, backup, etc.). The migration of sourcefile (A) 706 to target file (A) may have been declared as completed eventhough the target file (A) 710 may not comprise all of the data ofsource file (A) 706 that is to be migrated from source file (A) 706 totarget file (A) 710. For example, 405 MB out of 1 GB of data may havebeen migrated from source file (A) 706 to target file (A) 710, such that595 MB of data may still be pending for migration. In this way, thetarget file (A) 710 may appear to be accessible and/or completelymigrated even though pending data has yet to be migrated from sourcefile (A) 706 to target file (A) 710 (e.g., an indication of source file(A) 706 may be removed from source location 704 and/or target file (A)701 may appear to comprise the entire 1 GB of data). Additionally, arelationship 712 between target file (A) 710 and source file (A) 706 mayhave been specified. The relationship 712 may comprise fetch informationfor source file (A) 706, which may be used to access the source file (A)706 to satisfy I/O requests associated with target file (A) 710corresponding to data that has yet to be migrated from source file (A)706 to target file (A) 710.

The on-demand component 702 may receive the write request 714 associatedwith target file (A) 710 (e.g., a user may request to write new data tothe target file (A) 710, the user may request to overwrite data to thetarget file (A) 710 that may or may not be migrated so far). Theon-demand component 702 may perform the write request (write operation716) to generate written data. The on-demand component 702 may update718 the relationship 712 with a specification 720 that migrated datafrom the source file (A) 706 is not to overwrite the written data. Inthis way, a user may access and/or write to the target file (A) 710 eventhough target file (A) 710 may not comprise all of the data that is tobe migrated from the source file (A) 706 to the target file (A) 710.

FIG. 8 illustrates an example 800 of an on-demand component 802facilitating a read request 814 associated with a target file (A) 810.It may be appreciated that the target file (A) 810 may correspond tosource file (A) 806 at source location 804. In particular, target file(A) 810 may have been generated at target location 808 in response to arequest to migrate source file (A) 806 to target file (A) 810 (e.g.,move, cut/paste, copy, restore, backup, etc.). The migration of sourcefile (A) 806 to target file (A) may have been declared as completed eventhough the target file (A) 810 may not comprise all of the data ofsource file (A) 806 that is to be migrated from source file (A) 806 totarget file (A) 810. For example, 405 MB out of 1 GB of data may havebeen migrated from source file (A) 806 to target file (A) 810, such that595 MB of data may still be pending for migration. In this way, thetarget file (A) 810 may appear to be accessible and/or completelymigrated even though pending data has yet to be migrated from sourcefile (A) 806 to target file (A) 810 (e.g., an indication of source file(A) 806 may be removed from source location 804 and/or target file (A)801 may appear to comprise the entire 1 GB of data). Additionally, arelationship 812 between target file (A) 810 and source file (A) 806 mayhave been specified. The relationship 812 may comprise fetch information816 for source file (A) 806, which may be used to access the source file(A) 806 to satisfy I/O requests associated with target file (A) 810corresponding to data that has yet to be migrated from source file (A)806 to target file (A) 810.

The on-demand component 802 may receive the read request 814 associatedwith the target file (A) 810. In one example, the on-demand component802 may determine that the target file (A) 810 comprises read dataassociated with the read request 814, and thus may satisfy the readrequest 814 by provided access to the read data within the target file(A) 810. In another example, the on-demand component 802 may determinethat the target file (A) 810 does not comprise read data 820 associatedwith the read request 814. Thus, the read data 820 may be comprisedwithin the source file (A) 806. The on-demand component 802 may retrievefetch information 816 from the relationship 812 of the target file (A)810 and the source file (A) 806. The fetch information 816 may be usedto access the read data 820 within the source file (A) 806. Theon-demand component 802 may perform an on-demand operation 818 to fillthe target file (A) 810 with the read data 820 form the source file (A)806 based upon the fetch information 816. The read request 814 may beperformed upon the read data filled within the target file (A) 810. Inthis way, a user may access and/or read data associated with the targetfile (A) 810 regardless of whether the read data has yet been migratedfrom the source file (A) 806 to the target file (A) 810.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), EEPROM and/or flash memory, CD-ROMs, CD-Rs, CD-RWs, DVDs,cassettes, magnetic tape, magnetic disk storage, optical or non-opticaldata storage devices and/or any other medium which can be used to storedata. Computer readable media may also comprise communication media,which typically embodies computer readable instructions or other data ina modulated data signal such as a carrier wave or other transportmechanism (e.g., that has one or more of its characteristics set orchanged in such a manner as to encode information in the signal). Thecomputer readable medium can also be distributed (e.g., using aswitching fabric, such as used in computer farms) over a network-coupledcomputer system so that computer readable code is stored and executed ina distributed fashion.

Another embodiment (which may include one or more of the variationsdescribed above) involves a computer-readable medium comprisingprocessor-executable instructions configured to apply one or more of thetechniques presented herein. An exemplary computer-readable medium thatmay be devised in these ways is illustrated in FIG. 9, where theimplementation 900 comprises a computer-readable medium 908 (e.g., aCD-R, DVD-R, platter of a hard disk drive, flash drive, etc.), on whichis encoded computer-readable data 906. This computer-readable data 906in turn comprises a set of computer instructions 904 configured tooperate according to the principles set forth herein. In one suchembodiment, the processor-executable instructions 904 may be configuredto perform a method 902, such as at least some of the method 300 of FIG.3 or method 400 of FIG. 4, for example, as well as at least some of asystem, such as at least some of the system 500 of FIG. 5, for example.Many such computer-readable media may be devised by those of ordinaryskill in the art that are configured to operate in accordance with thetechniques presented herein.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

As used in this application, the terms “component,” “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentmay be, but is not limited to being, a process running on a processor, aprocessor, an object, an executable, a thread of execution, a program,and/or a computer. By way of illustration, both an application runningon a controller and the controller can be a component. One or morecomponents may reside within a process and/or thread of execution and acomponent may be localized on one computer and/or distributed betweentwo or more computers.

Furthermore, the claimed subject matter may be implemented as a method,apparatus, or article of manufacture using standard programming and/orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as may be used hereinis intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. Of course, those skilled inthe art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter.

It will be appreciated that the word “exemplary” is used herein to meanserving as an example, instance, or illustration. Any aspect or designdescribed herein as “exemplary” is not necessarily to be construed asadvantageous over other aspects or designs. Rather, use of the wordexemplary is intended to present concepts in a concrete fashion. Also asused herein, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or”. That is, unless specified otherwise, or clearfrom context, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A; X employs B; or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. In addition, the articles “a” and “an” as usedherein, including the appended claims, may generally be construed tomean “one or more” unless specified otherwise or clear from context tobe directed to a singular form.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure is intended to include such modifications and alterations. Inparticular regard to the various functions performed by the abovedescribed components (e.g., elements, resources, etc.), the terms usedto describe such components are intended to correspond, unless otherwiseindicated, to any component which performs the specified function of thedescribed component (e.g., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature of the disclosuremay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and/oradvantageous for any given or particular application. Furthermore, tothe extent that the terms “includes”, “having”, “has”, “with”, orvariants thereof are used in either the detailed description or theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.”

What is claimed is:
 1. A method for facilitating data object levelon-demand operations, comprising: receiving a request to migrate asource data object from a source location to a target location;generating a target data object corresponding to the source data objectat the target location, the target data object initially comprising lessthan all of the data of the source data object; specifying arelationship between the source data object and the target data object,the relationship specifying fetch information for the source dataobject; providing an indication, to a computing device, declaring thatmigration of the source data object to the target location as the targetdata object is completed, such that the target data object is exposed tothe computing device for I/O access, notwithstanding the target dataobject comprising less than all of the data of the source data object;providing a second indication to the computing device that the sourcedata object is not available for I/O access from the source locationafter the migration is declared completed, but while the target dataobject comprises less than all of the data of the source data object;responsive to receiving an I/O request, from the computing device, afterthe migration is declared completed, but while the target data objectcomprises less than all of the data of the source data object,performing an on-demand operation to satisfy the I/O request, theon-demand operation utilizing the fetch information specified by therelationship to fetch a first portion of data associated with the I/Orequest from the source data object not migrated to the target dataobject; receiving a write request associated with the target data objectwhile the target data object comprises less than all of the data of thesource data object; performing the write request upon the target dataobject to generate written data; and specifying within the relationshipthat migrated data from the source data object is not to overwrite thewritten data, at least some of the method implemented via a processor.2. The method of claim 1, comprising: obtaining a second portion of thedata associated with the I/O request from the target data object.
 3. Themethod of claim 1, the source data object corresponding to a source pathand the target data object corresponding to a target path different thanthe source path.
 4. The method of claim 3, the source path correspondingto a first volume and the target path corresponding to a second volumedifferent than the first volume.
 5. The method of claim 1, at least oneof the receiving an I/O request or the performing an on-demand operationoccurring during a non-migration state between the source data objectand the target data object.
 6. The method of claim 1, the request tomigrate the source data object corresponding to a source data objectcopy operation from the source location to the target location.
 7. Themethod of claim 1, the request to migrate the source data objectcorresponding to a source data object restoration operation from thesource location to the target location.
 8. The method of claim 1, thesource location corresponding to a first volume and the target locationcorresponding to a second volume different than the first volume.
 9. Themethod of claim 1, the I/O request comprising a read request.
 10. Themethod of claim 1, the request to migrate the source data objectcorresponding to a source data object move operation from the sourcelocation to the target location.
 11. A method for maintaining arelationship mapping at a target location, comprising: specifying afirst relationship, between a first source data object at a first sourcelocation and a first target data object at a target location, within arelationship mapping, the first relationship indicating the first targetdata object comprises less than all of the data of the first source dataobject that is to be migrated from the first source data object to thefirst target data object, the first relationship comprising fetchinformation for the first source data object; maintaining the firstrelationship within the relationship mapping based upon data migrationfrom the first source data object to the first target data object;providing an indication, to a computing device, declaring that migrationof the first source data object to the target location as the firsttarget data object is completed, such that the first target data objectis exposed to the computing device for I/O access, notwithstanding thefirst target data object comprising less than all of the data of thefirst source data object; providing a second indication to the computingdevice that the first source data object is not available for I/O accessfrom the first source location after the migration is declaredcompleted, but while the first target data object comprises less thanall of the data of the first source data object; and responsive toreceiving a first I/O request, from the computing device, while thefirst target data object comprises less than all of the data of thefirst source data object, performing an on-demand operation to satisfythe first I/O request, the on-demand operation utilizing the fetchinformation specified by the first relationship to fetch a first portionof data associated with the first I/O request from the first source dataobject not migrated to the first target data object, the on-demandoperation accessing a second portion of data associated with the firstI/O request from the first target data object, at least some of themethod implemented via a processor.
 12. The method of claim 11, thefirst I/O request comprising a read request.
 13. The method of claim 11,comprising: adding the first portion of data to the first target dataobject.
 14. The method of claim 11, at least one of the receiving afirst I/O request or the performing an on-demand operation occurringduring a non-migration state between the first source data object andthe first target data object.
 15. The method of claim 11, comprising:specifying a second relationship, between a second source data object ata second source location and a second target data object at the targetlocation, within the relationship mapping, the second relationshipindicating the second target data object comprises less than all of thedata of the second source data object, the second relationshipcomprising fetch information for the second source data object; andmaintaining the second relationship within the relationship mappingbased upon data migration from the second source data object to thesecond target data object.
 16. The method of claim 11, comprising:specifying a third relationship, between a third source data object atthe first source location and a third target data object at the targetlocation, within the relationship mapping, the third relationshipindicating the third target data object comprises less than all of thedata of the third source data object, the third relationship comprisingfetch information for the third source data object; and maintaining thethird relationship within the relationship mapping based upon datamigration from the third source data object to the third target dataobject.
 17. The method of claim 11, the relationship mapping comprisinga tree structure, the tree structure comprising source data objecthandles as indexes for respective relationships of the relationshipmapping.
 18. The method of claim 17, the tree structure comprising a B+tree.
 19. A system for facilitating data object level on-demandoperations, comprising: one or more processors; and memory comprisinginstructions that when executed by at least one of the one or moreprocessors implement at least some of: a migration component configuredto: receive a request to migrate a source data object from a sourcelocation to a target location; generate a target data objectcorresponding to the source data object at the target location, thetarget data object initially comprising less than all of the data of thesource data object; specify a relationship between the source dataobject and the target data object, the relationship specifying fetchinformation for the source data object; provide an indication, to acomputing device, declaring that migration of the source data object tothe target location as the target data object is completed, such thatthe target data object is exposed for I/O access, notwithstanding thetarget data object comprising less than all of the data of the sourcedata object; provide a second indication to the computing device thatthe source data object is not available for I/O access from the sourcelocation after the migration is declared completed, but while the targetdata object comprises less than all of the data of the source dataobject; and responsive to receiving an I/O request, from the computingdevice, after the migration is declared completed, but while the targetdata object comprises less than all of the data of the source dataobject, perform an on-demand operation to satisfy the I/O request, theon-demand operation utilizing the fetch information specified by therelationship to fetch a first portion of data associated with the I/Orequest from the source data object not migrated to the target dataobject; and an on demand component configured: receive a write requestassociated with the target data object while the target data objectcomprises less than all of the data of the source data object; performthe write request upon the target data object to generate written data;and specify within the relationship that migrated data from the sourcedata object is not to overwrite the written data.
 20. The system ofclaim 19, the target data object comprising a first single file and thesource data object comprising a second single file.
 21. The system ofclaim 19, the source location corresponding to a first volume and thetarget location corresponding to a second volume different than thefirst volume.
 22. The system of claim 19, the I/O request comprising aread request.
 23. The system of claim 19, the request to migrate thesource data object corresponding to at least one of: a source dataobject copy operation from the source location to the target location; asource data object restoration operation from the source location to thetarget location; or a source data object move operation from the sourcelocation to the target location.
 24. A non-transitory computer readablemedium comprising instructions which when executed perform a method forfacilitating on-demand operations comprising: providing an indication,to a computing device, declaring that migration of a source data objectfrom a source location to a target location as a target data object iscompleted, such that the target data object is exposed to the computingdevice for I/O access, notwithstanding the target data object comprisingless than all of the data of the source data object; providing a secondindication to the computing device that the source data object is notavailable for I/O access from the source location after the migration isdeclared completed, but while the target data object comprises less thanall of the data of the source data object; receiving a request, from thecomputing device, to access a portion of the target data object whilethe target data object comprises less than all of the data of the sourcedata object; responsive to determining that the requested portioncorresponds to a read request, then: consulting a relationshipassociated with the migration between the source data object and thetarget data object to determine a source path of the source data object;and performing an on-demand operation to retrieve data from the sourcedata object using the source path to satisfy the read request:responsive to determining that the requested portion corresponds to awrite request, then: performing the write request upon the target dataobject to generate written data; and specifying within the relationshipthat migrated data from the source data object is not to overwrite thewritten data.
 25. The non-transitory computer readable medium of claim24, the source location corresponding to a first volume.
 26. Thenon-transitory computer readable medium of claim 25, the target locationcorresponding to a second volume different than the first volume. 27.The non-transitory computer readable medium of claim 24, therelationship comprising at least one of a host identifier of the sourcelocation, an IP address of the source location, or a computing deviceidentifier of the source location.